Recently, a brushless DC motor has been used in an electric power tool which rotates a tool such as a drill or a driver by a motor thereby to perform the required work. The brushless DC motor is a DC (Direct-Current) motor having no brush (brush for communication), which uses coils (windings) on the stator side, and a permanent magnet on the rotor side, and applies the electric power driven by an inverter to the predetermined coil in order thereby to rotate a rotor. As an example of the brushless DC motor, for example, a brushless DC motor described in PTL 1 has been known. In this PTL 1, a switching element for switching on/off the current application to a coil wounded on a stator is arranged on a circular circuit board attached to the rear end side (the side opposite to an output shaft) of a motor. All the switching elements are mounted on a one-sided surface (surface on the rear side) of the circuit board, and abut on a heat radiating member fixed to a stator core separately from the circuit board for radiating the heat generated in the switching elements.
Recently, in an electric power tool which rotates and drives a tool such as a drill or a driver by a motor thereby to perform the required work, a fan for cooling the motor is provided. The fan is provided coaxially with the motor, and rotates with the rotation of the motor. Usually, the fan is provided on the rear end side of a rotational shaft of the motor or the front end side thereof, and a heat generating portion of the motor is cooled by the air flow generated by the fan. In an electric power tool using a brushless DC motor, since a rotor is rotated by supplying the electric power driven by an inverter to the predetermined coils in order, an inverter circuit composed by an output transistor is arranged, for example, at the rear of the motor, and the inverter circuit is also cooled by the air generated by the fan. Further, in PTL 2, a technology has been disclosed, in which a control transistor for a switch of an electric power tool is arranged on a heat sink, this heat sink is arranged near a battery, and the external air passes through the heat sink and the battery from an opening formed in a housing (lower portion of a handle portion) near the heat sink.